Complete the recursive formula of the arithmetic sequence $8, -5, -18, -31,...$. $d(1)=$
Explanation: The first term is $8$ and the common difference is $-13$. ${-13\,\curvearrowright}$ ${-13\,\curvearrowright}$ ${-13\,\curvearrowright}$ $8,$ $-5,$ $-18,$ $-31,...$ This is the recursive formula of $8, -5, -18, -31,...$ $\begin{cases} d(1)=8 \\\\ d(n)=d(n-1)+(-13) \end{cases}$